The present invention is directed to a hydropneumatic suspension system for a vehicle, in particular for the front axle of a tractor provided with a level control.
Due to the high load distribution they are subjected to, tractors often require a level control system. Depending on the load acting on the axle in question, the vehicle undergoes a spring compression or rebounding, and thus a lowering or lifting of the vehicle body. These variations are sensed by a level-control system, and the vehicle body is returned to its level position by regulating the pressure levels in the hydraulic suspension cylinders of the vehicle up or down, accordingly.
A very simple approach for a level-control system is described in German Patent Application DE 1 780 394 A1. However, the mode of operation of the level-control system it discusses no longer meets the requirements of today's level-control systems.
A hydropneumatic suspension system described in German Patent DE 42 42 448 C1, the entire disclosure of which is incorporated herein, represents a possible improvement. This system is specially conceived for vehicles having high load ratios, in particular for tractors having attachment means for add-on units. A load-sensing pump is used to create a suspension system that has a number of special advantages. This suspension system is able to be used quite advantageously in larger vehicles. However, when used in smaller tractors, i.e., lightweight tractors, it is typically underloaded.